1. Are your other contacts all using Communicator?
2. Does your OCMS server have the presence application installed?
3. Are your XDMS settings in your Oracle Communicator correctly set to your OCMS instance and HTTP port (typically 8888)?

As far as SIP underneath, when the Communicator needs to send presence information to other clients, it issues a PUBLISH message. When interested in presence information of other clients, it issues a SUBSCRIBE message. When receiving presence information from other clients, it receives a NOTIFY message.

For some background reading on SIP, I recommend RFC 3261 and RFC 3265.
http://www.ietf.org/rfc/rfc3261.txt
http://www.ietf.org/rfc/rfc3265.txt

Hi Adam.
The thing is that I´m using the sip-communicator client, a open source client, and as far as I can tell is exchanging the correct messages with the server but other users that are connected using Communicator, can´t see is Online but can call him. Other thing that I find odd is that I can send messages from the sip-communicator to others that are using the Communicator but can´t do the other way around... Do you know what is the problem?
The Presence server is installed and XDMS settings are correct.
Thanks,
Joel.

Joel,
I am hitting the same issue,were you able to resolve it.I am using Sip Communicator version 1.0-beta1-nightly.build.3364 and not able to get the user see each other's statuses.
It doesn't seem to work with any client except Oracle Communicator.